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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
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<body>
    <script>
        const a = 1;
        // a = 2; //此处会抱错，提示变量赋值给常数变量。
        console.log(a);
        const b = {
            c: 1,
            d: 2
        };
        // b = {//此处会抱错，提示变量已经赋值给常数变量
        //     c1: 1,
        //     c2: 3
        // };
        // console.log(b);
        b.e = 3;
        console.log(b); //可以新增属性
        b.d = 3333;
        console.log(b); //可以修改已经有的属性
    </script>
</body>

</html>